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Unformatted text preview: 02/20/2001 TUE 12:50 FAX 6434330 MOFFITT LIBRARY 001 ER 102 Harte/Fischer
Spring, 1998 MJDTERM EXAMINATION
March 10, 1998 This exam is open books and open notes. Anything you can lug into the classroom to help you is
acceptable as long as it is: a. non-addictive, b. quiet, c. odorless, and d. inanimate. The problems are assigned points that add up to 80. By coincidence, you also have 80 minutes to
do the exam, so you would be wise to allocate your time accordingly -- roughly one minute per point. Show all your work so you can get partial credit for “right idea but wrong answer”. Ifyou need a
number that you can’t ﬁnd or remember or derive, deﬁne a symbol for it and express your answer
in terms of that symbol. Then take a guess at its value -— it can’t hurt —- and substitute it in. If you don’t have time to complete a problem but think you know how to do it, describe the steps;
that way we have an excuse to give you partial credit. Don’t make your answers to the questions harder than necessary. There is nothing tricky or
cemplicated about these problems! Circle or underline your ﬁnal numerical answer to each problem. Either write your answer in a.
bluebook or, if you don’t have one, on 8.5" x 11” sheets of paper. In the latter case, be sure your
name is on every sheet not just the ﬁrst one, and staple them together. 02/20/2001 TUE 12:50 FAX 6434330 MOFFITT LIBRARY 002 BR 102 Midterm--Spn'ng, 1998
1. Using just the following numerical information: a. In the totality of living terrestrial biomass (mostly plants of course), the ratio of carbon to
nitrogen is about 50, b. In soil the ratio of dead organic carbon to dead organic nitrogen is typically about 20, c. The ratio of the carbon in the litter input to soil (falling dead leaves, etc.) to that of the
nitrogen in the litter input is about 12, d. The total terrestrial rate of net primary productivity is about 50 Gt(C)/y, e. The stock of carbon in living terrestrial biomass is about 600 Gt(C), f. The stock of organic carbon in soil is about ZOOOGt(C),
g. The stock of available inorganic nitrogen (ammonium and nitrate) in soil is about 5 Gt(N), and ignoring the relatively small contributions to the N cycle ﬁom N—ﬁxation and denitriﬁcation,
estimate the residence times of carbon and of nitrogen in living terrestrial biomass and the
residence times of organic carbon, organic nitrogen, and available inorganic nitrogen in soil. (5 X
6 = 30 pts.) 2. China now consumes about 840 million tons/y, about 20% more than does the US, but with 4 times the US population their per-capita rate of coal consumption is currently less than ours.
Suppose that about 100 years from now China’s per-capita rate of coal combustion increases to the same value as ours today, and its population doubles compares to today’s. Further, assume that the coal contains 2% sulﬁn’ by weight and is not “cleaned”, nor are scrubbers
used in the combustion of that coal. As a result, 1/2 of the sulﬁlr in the combusted coal converts
in the atmosphere over China to H2804 and this sulﬁiric acid falls as acid rain over a land area of 106 km2 in Eastern China. That land area receives on average 0.75 m of rain each year. i. How many tens of coal will China be consuming each year under these ﬁsture conditions? (4
pts.) ii. How many tons/y of sulﬁlr will be converted to sulﬁn‘ic acid and deposited over the speciﬁed
land area? (4 pts.) In units of grams/liter, what will be the S concentration of the rain that falls on the speciﬁed
area? (4 pts.) iv. How many molesfliter of S does this correspond to? (4 pts.) v. How many moles/liter ot‘H+ will be in the rain? (4 pts.) vi. What will the pH of the rain be? (4 pts.) 3. It was stated in class that the rate of flow of energy in the form of latent heat of vaporization from Earth’s surface to the atmosphere is approximately 80 Watts/square meter. Derive this
number by considering the energy (heat of vaporization) needed to evaporate the annual rainfall
on a typical square meter of the Earth’s surface. ( 26 pts.) ...
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